As the circuit density of modern semiconductor chips in modern computers has increased, there has been a greater need for more tightly packed signal and power connections between the modules carrying these chips and the circuit boards with which the chips interface. Also, this increased circuit density has led to a need for more direct power connections to the modules that carry the chips. As a result, circuit packages have been developed that employ a large central circuit board with semiconductor chip modules mounted on one side of the board and a small power supply board for each module mounted on the other side of the board. The chip modules and their power supply boards are each electrically connected to contact pads on their respective sides of the central board by resilient contact members. These contact members are mounted on interposer frames located between the modules and the central board and between the power supply boards and the central board. An example of an interposer frame with such contact members is shown in U.S. Pat. No. 5,061,192, assigned to the same assignee as the present invention, in which members 15 are mounted on an interposer frame 11 (FIGS. 2 to 4).
The large number of closely spaced contact pads and contact members located on a plurality of modules, boards and frames presents a problem of maintaining proper alignment of the contact pads with their respective contact members during assembly. Also, the modules, boards and frames must be restrained from tilting with respect to one another to insure an even pressure between all of the contact members and their pads, so that each contact member makes a good electrical connection with its pad.
Known assemblies for connecting electrical circuits on a plurality of stacked boards have not had the kind of alignment and pressure distribution features that are needed to form reliable electrical connections in the modern environment of high circuit density semiconductor chips. For instance, in U.S. Pat. No. 3,026,494, the stacked circuit boards and intermediate connector blocks are assembled by passing pins and bolts through holes in the corners of the circuit boards and in the end portions of the connector blocks. Then, nuts are threaded onto the corner bolts and each of the bolts is separately tightened against the top circuit board. While these bolts are being separately tightened, the circuit boards and connector blocks can easily become tilted with respect to one another, causing misalignment between the resilient contact arms on the connector blocks and their contact pads on the circuit boards. Also, the uneven pressure applied to the various contact members can result in faulty electrical connections between some of the members and the pads on the circuit boards.
Similar problems can occur in the assemblies shown in U.S. Pat. Nos. 3,904,934; 4,911,644; 4,932,883; 4,948,374; 4,969,826 and 5,076,794. In all of these assemblies, a plurality of nuts or bolts must be separately tightened, thus creating the likelihood of some misalignment and poor electrical contact. Of course, in the assembly of circuit boards and connectors in which the electrical contact pads are spaced relatively far apart and the resilient contact areas are of fairly large size, these alignment and contact problems are not as great as they are in assemblies containing high density electrical circuits and closely spaced contact pads.